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Home › Navigation › Navigation in Restricted Visibility
Operational guide · Operational procedure

Navigation in Restricted Visibility

Rule 19 operates when vessels are not in sight in or near restricted visibility: when taking radar action avoid, so far as possible, port alteration for a contact forward of the beam and alteration towards a contact abeam or abaft.

restricted visibilityCOLREG Rule 19radarfog

Operational Explanation

Rule 19 concerns vessels not in sight of one another when navigating in or near restricted visibility. Rule 19(d) has two distinct cautions: avoid, so far as possible, alteration to port for a vessel forward of the beam except when overtaking; and alteration towards a vessel abeam or abaft the beam. If actually in sight, apply the relevant Rules for vessels in sight.

Regulatory Reference

COLREG Rules 19 and 35: conduct and signals in restricted visibility. The category follows actual restriction of visibility, not darkness or adverse weather in isolation.

Scope of Application

Vessels not in sight of one another when navigating in or near restricted visibility. Radar acquisition alone does not make a vessel in sight.

Procedure / How to Complete It

  1. Determine whether the other vessel is actually in sight and which group of Rules applies.
  2. Proceed at safe speed with engines ready and enhanced lookout.
  3. Use radar plotting/ARPA and all available means to assess collision risk.
  4. If action is a course alteration, avoid so far as possible port for forward of beam except overtaking and towards for abeam/abaft.
  5. Apply Rule 19(e) for a fog signal forward of the beam or unavoidable close quarters and continue with extreme caution.

Practical Example

A radar target forward of the beam does not create a generic prohibition on turning towards it: the textual caution is against alteration to port, except when overtaking. For a target abeam/abaft, avoid alteration towards it.

What Typically Goes Wrong

Reducing Rule 19(d) to do not alter towards a contact forward of the beam, omitting the second branch, or treating darkness as a standalone restricted-visibility category.

Common Mistakes Mistake Library

MistakeConsequenceHow to Avoid It
Reducing Rule 19(d) to do not alter towards a contact forward of the beam, omitting the second branch, or treating darkness as a standalone restricted-visibility category.Incorrect operational decision or regulatory statusUse the primary reference and ship-specific procedure

What the PSCO Checks

Lookout, safe speed, in-sight/not-in-sight status, radar plotting, both Rule 19(d) branches, Rule 35 signals and Rule 19(e) action.

Operational Tips

Preparation checklist

FAQ

Does Rule 19 prohibit every turn towards a target forward?
No. For forward of the beam the caution is to avoid alteration to port, except when overtaking.
What about a target abeam or abaft?
Avoid, so far as possible, alteration towards that vessel.
Is darkness enough for Rule 19?
No. Actual restricted visibility and the vessels not being in sight are decisive.

Related Topics

COLREG in PracticeWatchkeeping

Last substantive revision of this page: 31 August 2026 · page fingerprint 3e63c72128a1